(1) Field of the Invention
The present invention relates to the treatment of molten slag, slag being withdrawn from a blast furnace for example, and particularly to the granulation of such molten slag. More specifically, this invention is directed to apparatus for treating molten slag with water to form a granulated product. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
It is known to mix the molten slag withdrawn from a furnace with water to form a solid product. Specifically, it is known to convey molten slag into a water stream to thereby produce a granulated product which, after drying, may be handled with relative ease. The foregoing has been accomplished by directing the molten slag into a trough through which a stream of water flows. The pressure and the rate of flow of the water must be sufficiently high to insure that the slag will be entrained therein and thus will flow along with the water to a filtration pit. Also, the quantity and temperature of the water must be selected so as to insure complete granulation.
To briefly elaborate on the foregoing, in order to insure complete granulation and to prevent the formation of deposits of granulated slag in the trough, a stream of pressurized water must be employed. In actual practice, in the treatment of four to seven tons of slag per minute, it was not uncommon in the prior art for 2000 m.sup.3 of water per hour to be required. The use of this much water, and the power requirements incident to the pumping thereof, constitute obvious disadvantages from both economic and environmental viewpoints. It is also to be observed that, since the water employed for granulation must be re-separated from the mixture in order to obtain a filtered granulated slag with a low moisture content, a reduction in the quantity of granulation water would enable the employment of filtration installations of a more modest size than presently required.
The average size of granules of slag produced in the above-described method is known to be partly a direct function of the temperature of the water with which the molten slag is mixed. Thus, the average size of the slag particles formed during the granulation process will increase with an increase in the temperature of the granulation water. In order to produce a granulated product having a relatively large average grain size with a comparatively low proportion of fines, which is more readily marketable and from which water may be more easily separated, relatively high temperature granulation water should be employed. However, if the granulation water is too hot the final temperature of the granulated slag-water mixture, hereinafter referred to as the "pulp", will be higher than can be safely handled by apparatus downstream of the mixing station. Accordingly, in the prior art granulation water at reduced temperature has been employed and the industry has been reconciled to the achievement of a smaller average grain size than desired for the slag and a comparatively high proportion of fines.